1. Field of the Invention
The present invention relates generally to a foam article having absorbing characteristics on one side and non-absorbing characteristics on the other side and the product from which the foam article is made. This invention also relates to the method for making the foam articles. More particularly, the foam article is an open cell expanded plastic foam on one side of the article and closed cells on the other side of the article.
2. Description of the Prior Art
Expanded plastic foams have long been known. In particular, various expanded open cell plastic foams have a wide range of uses especially for absorbing liquids. Such plastic foams may be produced by extruding a thermoplastic synthetic resin together with a blowing agent, in particular a gaseous blowing agent, from an annular or slot die or co-extrusion die. The blowing agent is distributed throughout the melted plastic and upon extrusion expands so that very fine bubbles form in the plastic article to cause expansion of the plastic. Smaller or larger bubbles are obtained depending on the process conditions with regard to the temperature and extrusion rate. In the typical process the temperature gradient across the expanded article results in cooler outer surfaces on each side of the expanded foam that results in the outer surfaces having closed cells. Such foams have closed cells on the outside surfaces of the foam article and open cells in the interior of the article. These foams, while having excellent insulating properties do not have very useful absorbing properties.
An expanded plastic foam in which the cells are open, i.e., have a through passage, shows completely different characteristics. Open cell expanded plastic foams are capable of absorbing liquids similar to a sponge. In the case of such open cell foams, the cells are connected to one another via the gas phase.
Various methods are available to obtain expanded plastic foams having open cells. One method of obtaining an open cell structure is to exert mechanical pressure on the expanded plastic foam thereby opening the previously closed cells. In this method the compression forms open cells on the interior of the expanded foam and closed cells on the outsides of the expanded foam. However, mechanical compression of the outside of an extruded, expanded foam article such as that disclosed in Hardy, U.S. Pat. No. 3,443,007, does not provide a foam structure having open cells available for absorption. Another mechanical process for the formation of open cells is to stretch the extrudate as it exits the extruder and expands from the extrusion die to form a unique structure as shown in U.S. Pat. No. 6,071,580 to Bland, et al.
Chemical processing is also used to produce an open cell structure, such as by using an excess of nucleating agent without a blowing agent as taught in U.S. Pat. No. 5,618,853 to Vonken, et al. However, such structure does not provide a foam structure having both an open cell and a closed cell structure. The patents to Jou, et al., U.S. Pat. No. 4,776,356 and U.S. Pat. No. 3,386,877 to Skochdopole, et al., teach selectively varying the temperature to obtain both open and closed cells in a foamed plastic article.
It is therefore desirable to provide an expanded foam article that has absorbing characteristics on one side and non-absorbing characteristics on the other side and to provide a method for making such an article.